The present invention relates to a micromachine switch for use in millimeter wave circuits and microwave circuits.
Switch devices for use in millimeter wave circuits and microwave circuits include PIN diode switches, HEMT switches, and micromachine switches. Micromachine switches in particular suffer a smaller loss, are less costly, and have a lower power requirement than the other switch devices.
One conventional micromachine switch is disclosed in Japanese laid-open patent publication No. 9-17300, for example. FIG. 1(A) of the accompanying drawings is a plan view of the conventional micromachine switch. FIG. 1(B) is a cross-sectional view taken along line I(B)xe2x80x94I(B) of FIG. 1(A). FIG. 1(C) is a cross-sectional view taken along line I(C)xe2x80x94I(C) of FIG. 1(A). FIG. 1(D) is a cross-sectional view taken along line I(D)xe2x80x94I(D) of FIG. 1(A).
As shown in FIG. 1(A), high-frequency signal lines 101a, 101b spaced from each other by a small gap are disposed on substrate 110. Lower electrode 111 is disposed on substrate 110 at a position spaced from high-frequency signal lines 101a, 101b. Post 112 is disposed on substrate 110 at a position on a line extending from the gap between high-frequency signal lines 101a, 101b through lower electrode 111.
Arm 113 has a proximal end fixedly mounted on an upper surface of post 112. Arm 113 extends from the upper surface of post 112 over lower electrode 111 to a position above the gap between high-frequency signal lines 101a, 101b. Arm 113 is made of an insulating material.
Upper electrode 114 is disposed on an upper surface of arm 113. Upper electrode 114 extends from a position above post 112 to a position above lower electrode 111.
Contact 115 is disposed on a lower surface of the distal end of arm 113. Contact 115 extends from a position above the end of high-frequency signal line 101a over the gap to a position above the end of high-frequency signal line 101b. 
Control signal line 102 is connected to lower electrode 111 for applying a control signal to change connected states of high-frequency signal lines 101a, 101b to lower electrode 111.
When a positive voltage, for example, is applied as the control signal to lower electrode 111, positive charges are generated on the upper surface of lower electrode 111, and negative charges are developed on the lower surface of upper electrode 114 which confronts lower electrode 111 due to electrostatic induction. Upper electrode 114 is now attracted to lower electrode 111 under attractive forces developed therebetween. Arm 113 is curved to displace contact 115 downwardly. When contact 115 is brought into contact with both high-frequency signal lines 101a, 101b, high-frequency signal lines 101a, 101b are connected to each other by contact 115 in a high-frequency fashion.
When the positive voltage is no longer applied to lower electrode 111, since no attractive forces are developed between upper and lower electrodes 114, 111, contact 115 returns to its position spaced from high-frequency signal lines 101a, 101b under recovering forces of arm 113. High-frequency signal lines 101a, 101b are now disconnected from each other.
The conventional micromachine switch shown in FIG. 1 has a complex three-dimensional structure because post 112 and arm 113 are required to support contact 115, other than contact 115 for connecting and disconnecting high-frequency signal lines 101a, 101b and also because lower electrode 111 and upper electrode 114 are required control displacement of contact 115. A complex fabrication process composed of many steps is needed to manufacture the micromachine switch of the complex structure.
The present invention has been made in an attempt to solve the above problems. It is an object of the present invention to provide a micromachine switch of a simple structure.
In order to achieve the above object, a micromachine switch according to the present invention has first and second high-frequency signal lines having their respective ends spaced from each other, a cantilever fixed to the end of either the first or the second high-frequency signal line and extending to a position above the end of the other high-frequency signal line, the cantilever including an electrically conductive member, first insulating means disposed on the first high-frequency signal line, second insulating means disposed in an area where the cantilever and the other high-frequency signal line confront each other, and a first control signal line connected between the end of the first high-frequency signal line and the first insulating means, for applying the control signal which is represented by DC voltage level variations.
An arrangement of the first insulating means comprises a capacitor.
An arrangement of the second insulating means comprises an insulating film disposed on at least one of a lower surface of the cantilever and an upper surface of the other high-frequency signal line.
The cantilever has both a function as a movable contact and a function as a support means for supporting the movable contact. The cantilever 11 functionally corresponds to contact 115, arm 113, and post 112 of the conventional micromachine switch, and the former is of a simpler structure than the latter.
Since the control signal is applied to the first or second high-frequency signal line to control operation of cantilever, lower electrode 111 and upper electrode 114 which have heretofore been required are no longer necessary. For this reason, the micromachine switch is thus further simple in structure.
While the first insulating means disposed on the first high-frequency signal line and the second insulating means for providing a capacitive coupling are indispensable according to the present invention, the micromachine switch is of a simple structure as a whole according to the present invention.
The micromachine switch may further comprise first high-frequency signal blocking means connected to the first control signal line, for blocking the passage of a high-frequency signal flowing through the first and second high-frequency signal lines.
A first arrangement of the first high-frequency signal blocking means comprises a high-impedance line having an end connected between the end of the first high-frequency signal line on which the first insulating means is disposed and the first insulating means, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, and a low-impedance line having an end connected to the other end of the high-impedance line and an opposite end which is open, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance smaller than the characteristic impedance of the high-impedance line, the first control signal line being connected to the other end of the high-impedance line.
A second arrangement of the first high-frequency signal blocking means comprises a high-impedance line having an end connected between the end of the first high-frequency signal line on which the first insulating means is disposed and the first insulating means, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, and a capacitor having an electrode connected to the other end of the high-impedance line and another electrode to ground, the first control signal line being connected to the other end of the high-impedance line.
A third arrangement of the first high-frequency signal blocking means comprises an inductive element.
A fourth arrangement of the first high-frequency signal blocking means comprises a resistive element having an impedance sufficiently larger than the characteristic impedance of the first or second high-frequency signal line.
The resistive element may be inserted in series in the first control signal line. Alternatively, the resistive element may have an end connected to the first control signal line and another end which is open.
The first high-frequency signal blocking means in the first control signal line is effective to prevent the high-frequency signal from leaking to the first control signal line.
The micromachine switch may further comprise a second control signal line connected to the second high-frequency signal line on which the first insulating means is not disposed, for charging and discharging electric charges generated by electrostatic induction, and second high-frequency signal blocking means connected to the second control signal line, for blocking the passage of the high-frequency signal flowing through the first and second high-frequency signal lines.
A first arrangement of the second high-frequency signal blocking means comprises a high-impedance line having an end connected to the second high-frequency signal line on which the first insulating means is not disposed, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, and a low-impedance line having an end connected to the other end of the high-impedance line and an opposite end which is open, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance smaller than the characteristic impedance of the high-impedance line, the second control signal line being connected to the other end of the high-impedance line.
A second arrangement of the second high-frequency signal blocking means comprises a high-impedance line having an end connected to the second high-frequency signal line on which the first insulating means is not disposed, and having a line length which is about xc2xc of the wavelength of the high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, and a capacitor having an electrode connected to the other end of the high-impedance line and another electrode to ground, the second control signal line being connected to the other end of the high-impedance line.
A third arrangement of the second high-frequency signal blocking means comprises an inductive element.
A fourth arrangement of the second high-frequency signal blocking means comprises a resistive element having an impedance sufficiently larger than the characteristic impedance of the first or second high-frequency signal line.
The resistive element may be inserted in series in the second control signal line. Alternatively, the resistive element may have an end connected to the second control signal line and another end which is open.
As electric charges generated by electrostatic induction are charged and discharged through the second control signal line, the micromachine switch performs stable switching operation and has an increased switching speed. The second high-frequency signal blocking means in the second control signal line is effective to prevent the high-frequency signal from leaking to the second control signal line.
The micromachine switch may further comprise a first high-impedance line having an end connected between the end of the first high-frequency signal line on which the first insulating means is disposed and the first insulating means, and having a line length which is about xc2xc of the wavelength of a first or second high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, a second high-impedance line having an end connected to the second high-frequency signal line on which the first insulating means is not disposed, and having a line length which is about xc2xc of the wavelength of the first or second high-frequency signal and a characteristic impedance larger than the characteristic impedance of the first or second high-frequency signal line, and a capacitor having an electrode connected to the other end of the first high-impedance line and another electrode to the other end of the second high-impedance line, the other end of the first high-impedance line being connected to the first control signal line and the other end of the second high impedance line being connected to ground.
The first high-impedance line, the capacitor, and the ground jointly make up first high-frequency signal blocking means. The second high-impedance line connected to ground provides second first high-frequency signal blocking means.
The micromachine switch further comprises third insulating means disposed on the second high-frequency signal line on which the first insulating means is not disposed, a second control signal line connected between the end of the first or second high-frequency signal line on which the third insulating means is disposed and the third insulating means, for applying a constant voltage having a polarity opposite to the control signal, and second high-frequency signal blocking means connected to the second control signal line, for blocking the passage of a high-frequency signal flowing through the first and second high-frequency signal lines, the arrangement being such that a DC voltage between the second and third insulating means is kept at the level of the constant voltage.
If a predetermined voltage is applied to the high-frequency signal line to which the control signal is not applied, then the magnitude of the voltage of the control signal can be reduced by the predetermined voltage.
According to the present invention, there is provided a method of manufacturing a micromachine switch, comprising the steps of forming, on a substrate, a first high-frequency signal line, a third high-frequency signal line having an end spaced from an end of the first high-frequency signal line, and a control signal line connected to the third high-frequency signal line, forming a sacrificial layer in at least a region extending from a gap between the first and third high-frequency signal lines to the end of the third high-frequency signal line, forming a first insulating film on a portion of the sacrificial layer which confronts the end of the third high-frequency signal line, and a second insulating film on the other end of third high-frequency signal line, forming a cantilever of metal in a region extending from the end of the first high-frequency signal line to the first insulating film on the sacrificial layer, and a fourth high-frequency signal line extending from an upper surface of the second insulating film onto the substrate, and removing the sacrificial layer.
According to the present invention, there is also provided a method of manufacturing a micromachine switch, comprising the steps of forming, on a substrate, a fifth high-frequency signal line, a second high-frequency signal line having an end spaced from an end of the fifth high-frequency signal line, and a control signal line connected to the fifth high-frequency signal line, forming a sacrificial layer in at least a region extending from a gap between the fifth and second high-frequency signal lines to the end of the second high-frequency signal line, forming a first insulating film on a portion of the sacrificial layer which confronts the end of the second high-frequency signal line, and a second insulating film on the other end of fifth high-frequency signal line, forming a cantilever of metal in a region extending from the end of the fifth high-frequency signal line to the first insulating film on the sacrificial layer, and a sixth high-frequency signal line extending from an upper surface of the second insulating film onto the substrate, and removing the sacrificial layer.
The micromachine switch can thus be manufactured in a small number of steps.